Metal Working Fluid

ABSTRACT

The present invention relates to a metal working fluid comprising abase oil having a viscosity index of more than 110 according to ASTM D 2270 and a pour point of less than −40° C. according to ASTM D 97. Preferably the base oil is a Fischer-Tropsch derived oil. Preferably, the base oil has a kinematic viscosity at 100° C. of between 2 and 3 mm 2 /s, according to ASTM D 445. Further, the base oil preferably has a flash point of more than 170° C., preferably more than 175° C., most preferably more than 180° C., according to ASTM D 92.

The present invention relates to a metal working fluid comprising a base oil and one or more additives. The present invention further relates to the use of the metal working fluid as a metal working fluid, in particular for high speed machining.

Metal working fluids are well known in practice and are used in metal working such as cutting, grinding, rolling, drawing and forging. In this respect reference is made to D. Klamann, Lubricants and related products, Verlag Chemie GmbH, Weinheim, Germany, 1984, pages 351-383, which is hereby incorporated by reference. An example of a metal working fluid (or ‘cutting oil’) has been described in U.S. Pat. No. 5,958,849.

A problem with known metal working fluids is that the base oil forming part thereof tends to evaporate too quickly thereby resulting in possibly damaging the metal working gear. This problem is even more pertinent in high speed machining, resulting in higher working temperatures thereby expediting the evaporation of (components of) the metal working fluid. High speed machining is a well known term in metal working technical area. Examples of apparatuses used in high speed machining are described in US20050254937 and U.S. Pat. No. 5,072,948.

It is an object of the present invention to avoid or at least minimize the above problem.

It is a further object of the present invention to provide an alternative metal working fluid.

One or more of the above of other objects is achieved by the present invention, by providing a metal working fluid comprising a base oil having a viscosity index of more than 110 according to ASTM D 2270 and a pour point of less than −40° C. according to ASTM D 97.

The invention is also directed to the use of said metal working fluid for high speed machining.

Surprisingly, the Applicants have found that a base oil with the above properties shows an excellent evaporation loss at different temperatures, thereby enabling a metal working fluid to be compounded with improved properties as compared to known metal working fluids. A further advantage of the present invention is that the metal working fluid comprising a base oil with the indicated properties has a relative high flash point, resulting in an improved safety during use of the metal working fluid. According to the present invention, metal working fluids may be obtained having a flash point (according to ASTM D 92) above 170° C.

An even further advantage of the present invention is that, using the indicated base oil for compounding the metal working fluid according to the present invention, a substantially chloride-free and non-emulsifying finished metal working fluid may be obtained. The metal working fluid may contain one or more additives.

This property makes the metal working fluid especially suited for use in high speed machining. The present invention relates to the use of the metal working fluid composition according to the present invention as a metal working fluid, in particular for high speed machining, i.e. above 8000 turns per minute, preferably above 10000 turns per minute. The rotary machine is provided with a hollow shaft through which the metal working fluid can flow to a machine tool mounted on said shaft.

The invention is also directed to a high speed grinding operation in which the grinding operation is performed using a grinding stone at a speed of between 50 and 200 m/s, more preferably above 100 m/s. This speed is defined as the relative velocity between the grinding tool and the metal object to be worked on at their contact point. The upper limit for this speed will depend on the design of the apparatuses wherein the desire is to achieve higher speeds. At present this value will be below 200 m/s, but higher speeds are expected for future machines.

The invention is also directed to high speed machining performed with a cutting tool as in for example reaming, turning and milling. High speed operation depends on type of material used. It can range from 50 m/min to 10000 m/min. The cutting speed at which an operation is defined as high speed machining will depend on the type of material of the machined material. High speed machining will be above 2000 m/min for polymer type material and aluminium, above 1000 m/min for bronze, above 900 m/min for cast iron, above 700 m/min for steel, above 200 for titanium and above 60 m/min for a nickel based allow.

The metal working fluid is preferably provided to the high speed rotary machine at a pressure of above 15 bar, preferably between 20 and 60 bar. This pressure is required to result in a desirably high flow of the metal working fluid through for example hollow shaft.

The person skilled in the art will readily understand what is meant with the term “base oil”. The base oil used according to the present invention may be obtained by hydroisomerisation of a paraffinic wax, preferably followed by some type of dewaxing, such as solvent or catalytic dewaxing. Preferably, the paraffinic wax is a Fischer-Tropsch derived wax, because of its purity and high paraffinic content. The base oil as obtained from the Fischer-Tropsch wax is furthermore advantageous because it has practically no aromatic content, no detectable smell and it has a crystal clear color as expressed by ASTM D 156 as +20.

Examples of Fischer-Tropsch processes which for example can be used to prepare the above-described Fischer-Tropsch derived base oil are the so-called commercial Slurry Phase Distillate technology of Sasol, the Shell Middle Distillate Synthesis Process and the “AGC-21” Exxon Mobil process. These and other processes are for example described in more detail in EP-A-776 959, EP-A-668 342, U.S. Pat. No. 4,943,672, U.S. Pat. No. 5,059,299, WO-A-9934917 and WO-A-9920720. Typically these Fischer-Tropsch synthesis products will comprise hydrocarbons having 1 to 100 and even more than 100 carbon atoms. This hydrocarbon product will comprise normal paraffins, iso-paraffins, oxygenated products and unsaturated products. If base oils are one of the desired iso-paraffinic products it may be advantageous to use a relatively heavy Fischer-Tropsch derived feed. The relatively heavy Fischer-Tropsch derived feed has at least 30 wt %, preferably at least 50 wt %, and more preferably at least 55 wt % of compounds having at least 30 carbon atoms. Furthermore the weight ratio of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms of the Fischer-Tropsch derived feed is preferably at least 0.2, more preferably at least 0.4 and most preferably at least 0.55. Preferably the Fischer-Tropsch derived feed comprises a C₂₀+ fraction having an ASF-alpha value (Anderson-Schulz-Flory chain growth factor) of at least 0.925, preferably at least 0.935, more preferably at least 0.945, even more preferably at least 0.955. Such a Fischer-Tropsch derived feed can be obtained by any process, which yields a relatively heavy Fischer-Tropsch product as described above. Not all Fischer-Tropsch processes yield such a heavy product. An example of a suitable Fischer-Tropsch process is described in WO-A-9934917.

The Fischer-Tropsch derived product will contain no or very little sulphur and nitrogen containing compounds. This is typical for a product derived from a Fischer-Tropsch reaction, which uses synthesis gas containing almost no impurities. Sulphur and nitrogen levels will generally be below the detection limits, which are currently 5 ppm for sulphur and 1 ppm for nitrogen respectively.

The process will generally comprise a Fischer-Tropsch synthesis, a hydroisomerisation step and an optional pour point reducing step, wherein said hydroisomerisation step and optional pour point reducing step are performed as:

-   (a) hydrocracking/hydroisomerisating a Fischer-Tropsch product, -   (b) separating the product of step (a) into at least one or more     distillate fuel fractions and a base oil fraction.

Optionally the pour point of the base oil is further reduced in a step (c) by means of solvent or preferably catalytic dewaxing of the oil obtained in step (b) to obtain oil having the preferred low pour point.

The hydroconversion/hydroisomerisation reaction of step (a) is preferably performed in the presence of hydrogen and a catalyst, which catalyst can be chosen from those known to one skilled in the art as being suitable for this reaction of which some will be described in more detail below. The catalyst may in principle be any catalyst known in the art to be suitable for isomerising paraffinic molecules. In general, suitable hydroconversion/hydroisomerisation catalysts are those comprising a hydrogenation component supported on a refractory oxide carrier, such as amorphous silica-alumina (ASA), alumina, fluorided alumina, molecular sieves (zeolites) or mixtures of two or more of these. One type of preferred catalysts to be applied in the hydroconversion/hydroisomerisation step in accordance with the present invention are hydroconversion/hydroisomerisation catalysts comprising platinum and/or palladium as the hydrogenation component. A very much preferred hydroconversion/hydroisomerisation catalyst comprises platinum and palladium supported on an amorphous silica-alumina (ASA) carrier. The platinum and/or palladium is suitably present in an amount of from 0.1 to 5.0% by weight, more suitably from 0.2 to 2.0% by weight, calculated as element and based on total weight of carrier. If both present, the weight ratio of platinum to palladium may vary within wide limits, but suitably is in the range of from 0.05 to 10, more suitably 0.1 to 5. Examples of suitable noble metal on ASA catalysts are, for instance, disclosed in WO-A-9410264 and EP-A-0 582 347. Other suitable noble metal-based catalysts, such as platinum on a fluorided alumina carrier, are disclosed in e.g. U.S. Pat. No. 5,059,299 and WO-A-9220759.

A second type of suitable hydroconversion/hydroisomerisation catalysts are those comprising at least one Group VIB metal, preferably tungsten and/or molybdenum, and at least one non-noble Group VIII metal, preferably nickel and/or cobalt, as the hydrogenation component. Both metals may be present as oxides, sulphides or a combination thereof. The Group VIB metal is suitably present in an amount of from 1 to 35% by weight, more suitably from 5 to 30% by weight, calculated as element and based on total weight of the carrier. The non-noble Group VIII metal is suitably present in an amount of from 1 to 25 wt %, preferably 2 to 15 wt %, calculated as element and based on total weight of carrier. A hydroconversion catalyst of this type which has been found particularly suitable is a catalyst comprising nickel and tungsten supported on fluorided alumina.

The above non-noble metal-based catalysts are preferably used in their sulphided form. In order to maintain the sulphided form of the catalyst during use some sulphur needs to be present in the feed. Preferably at least 10 ppm and more preferably between 50 and 150 ppm of sulphur is present in the feed.

A preferred catalyst, which can be used in a non-sulphided form, comprises a non-noble Group VIII metal, e.g., iron, nickel, in conjunction with a Group IB metal, e.g., copper, supported on an acidic support. Copper is preferably present to suppress hydrogenolysis of paraffins to methane. The catalyst has a pore volume preferably in the range of 0.35 to 1.10 ml/g as determined by water absorption, a surface area of preferably between 200-500 m²/g as determined by BET nitrogen adsorption, and a bulk density of between 0.4-1.0 g/ml. The catalyst support is preferably made of an amorphous silica-alumina wherein the alumina may be present within wide range of between 5 and 96 wt %, preferably between 20 and 85 wt %. The silica content as SiO₂ is preferably between 15 and 80 wt %. Also, the support may contain small amounts, e.g., 20-30 wt %, of a binder, e.g., alumina, silica, Group IVA metal oxides, and various types of clays, magnesia, etc., preferably alumina or silica.

The preparation of amorphous silica-alumina microspheres has been described in Ryland, Lloyd B., Tamele, M. W., and Wilson, J. N., Cracking Catalysts, Catalysis: volume VII, Ed. Paul H. Emmett, Reinhold Publishing Corporation, New York, 1960, pp. 5-9.

The catalyst is prepared by co-impregnating the metals from solutions onto the support, drying at 100-150° C., and calcining in air at 200-550° C. The Group VIII metal is present in amounts of about 15 wt % or less, preferably 1-12 wt %, while the Group IB metal is usually present in lesser amounts, e.g., 1:2 to about 1:20 weight ratio respecting the Group VIII metal.

A typical catalyst is shown below:

Ni, wt % 2.5-3.5 Cu, wt % 0.25-0.35 Al₂O₃—SiO2 wt % 65-75 Al₂O₃ (binder) wt % 25-30 Surface Area 290-325 m²/g Pore Volume (Hg) 0.35-0.45 ml/g Bulk Density 0.58-0.68 g/ml

Another class of suitable hydroconversion/hydroisomerisation catalysts are those based on zeolitic materials, suitably comprising at least one Group VIII metal component, preferably Pt and/or Pd, as the hydrogenation component. Suitable zeolitic and other aluminosilicate materials, then, include Zeolite beta, Zeolite Y, Ultra Stable Y, ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-48, MCM-68, ZSM-35, SSZ-32, ferrierite, mordenite and silica-aluminophosphates, such as SAPO-11 and SAPO-31. Examples of suitable hydroisomerisation/hydroisomerisation catalysts are, for instance, described in WO-A-9201657. Combinations of these catalysts are also possible. Very suitable hydroconversion/hydroisomerisation processes are those involving a first step wherein a zeolite beta based catalyst is used and a second step wherein a ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-48, MCM-68, ZSM-35, SSZ-32, ferrierite, mordenite based catalyst is used. Of the latter group ZSM-23, ZSM-22 and ZSM-48 are preferred. Examples of such processes are described in US-A-20040065581, which disclose a process comprising a first step catalyst comprising platinum and zeolite beta and a second step catalyst comprising platinum and ZSM-48.

In step (a) the feed is contacted with hydrogen in the presence of the catalyst at elevated temperature and pressure. The temperatures typically will be in the range of from 175 to 380° C., preferably higher than 250° C. and more preferably from 300 to 370° C. The pressure will typically be in the range of from 10 to 250 bar and preferably between 20 and 80 bar. Hydrogen may be supplied at a gas hourly space velocity of from 100 to 10000 Nl/l/hr, preferably from 500 to 5000 Nl/l/hr. The hydrocarbon feed may be provided at a weight hourly space velocity of from 0.1 to 5 kg/l/hr, preferably higher than 0.5 kg/l/hr and more preferably lower than 2 kg/l/hr. The ratio of hydrogen to hydrocarbon feed may range from 100 to 5000 Nl/kg and is preferably from 250 to 2500 Nl/kg.

The conversion in step (a) as defined as the weight percentage of the feed boiling above 370° C. which reacts per pass to a fraction boiling below 370° C., is at least 20 wt %, preferably at least 25 wt %, but preferably not more than 80 wt %, more preferably not more than 65 wt %. The feed as used above in the definition is the total hydrocarbon feed fed to step (a), thus also any optional recycle of a high boiling fraction which may be obtained in step (b).

In step (b) the product of step (a) is preferably separated into one or more distillate fuels fractions and a base oil or base oil precursor fraction having the desired viscosity properties. If the pour point is not in the desired range the pour point of the base oil is further reduced by means of a dewaxing step (c), preferably by catalytic dewaxing. In such an embodiment it may be a further advantage to dewax a wider boiling fraction of the product of step (a). From the resulting dewaxed product the base oil and oils having a desired viscosity can then be advantageously isolated by means of distillation. The final boiling point of the feed to the dewaxing step (c) may be up to the final boiling point of the product of step (a).

According to a preferred embodiment of the present invention, the base oil has a viscosity index of more than 115, advantageously more than 120, preferably more than 125, more preferably below 140, most preferably between 115-140. Also, the base oil preferably has a pour point of less than −50° C. Further, the base oil preferably has a kinematic viscosity at 100° C. of between 1-4 mm²/s, preferably between 2 and 3 mm²/s, according to ASTM D 445. This results in even more advantageous flash point and evaporation loss values.

It is especially preferred that the base oil has a flash point of more than 170° C., preferably more than 175°, most preferably more than 180° C., according to ASTM D 92.

Further it is preferred that the base oil has a Noack Volatility at 150° C. of less than 4, preferably less than 3, most preferably less than 2, according to modified CEC L40 A93.

Preferably, the base oil used in the present invention has a delta FBP-IBP (Distillation range between IBP and FBP determined according to ASTM D 2887) below 150° C., preferably below 130° C., more preferably below 120° C.

Further it is preferred according to the present invention that the base oil has a Delta Distillation value (95 wt %-5 wt %) of less than 130° C., preferably less than 100° C., even more preferably less than 95° C., the distillation values being determined according to ASTM D 2888.

The person skilled in the art will readily understand that various additives may be added to the metal working fluid according to the present invention, such as antioxidants, antimisting agents, metal deactivators, dyes, etc. Examples of suitable additives can be found in the above referenced “Lubricants and related products” of D. Klamann. Preferably between 1 and 15 wt % of an ester compounds is present. Examples of suitable ester compounds are rapeseed oil and pentaerythritol ester. Preferably a sulphur-containing compound is present in an amount of between 0.5 to 10 wt %. Examples of suitable sulphur containing compounds are sulfurized esters and polysulfures.

The metal working fluid according to the present invention may comprise different types of base oils, such as mineral oils, polyalphaolefins, esters, polyalkylenes, alkylated aromatics, hydrocrackates and solvent-refined base oils or their mixtures. However, preferably the metal working fluid comprises at least 80 wt % of the base oil of the base oil meeting the requirements of claim 1. It is even more preferred that the base oil component is exclusively the base oil meeting the requirements of claim 1. Even more preferably the base oil component is practically only the above described Fischer-Tropsch derived base oil. With practically is meant that the improved properties of the metal working fluid are achieved by this base oil. More especially, practically means that between 95 and 100 wt %, most especially 100 wt % of the base oil is the Fischer-Tropsch derived base oil.

Hereafter, the present invention will be further illustrated by making use of the following non-limiting examples.

EXAMPLE 1

From residue “R” as obtained according to Example 1 of EP-A-1 366 135 a Fischer-Tropsch derived distillation fraction was isolated having the properties as listed in Table 1. The wax content was 27.1 wt % as determined after solvent dewaxing at a dewaxing temperature of −27° C. Table 1. Feed to catalytic dewaxing

TABLE 1 Feed to catalytic dewaxing Congealing point  45° C. Density at 70° C. 0.796 IBP wt % distilled 362° C. 10 412° C. 50 462° C. 70 487° C. 90 519° C. FBP 573° C.

The above distillate fraction was contacted with a dewaxing catalyst consisting of 0.7 wt % platinum, 25 wt % ZSN-12 and a silica binder. The dewaxing conditions were 40 bar hydrogen, WHSV=1.0 kg/l.h, and a hydrogen gas rate of 500 Nl/kg feed and a temperature of 315° C. From the dewaxed oil a base oil fraction was isolated by distillation having the properties as listed in Table 2.

EXAMPLES 2

A further Fischer-Tropsch derived base oil according to the present invention was obtained by the same process as Example 1, but by isolating a slightly different distillation fraction. The properties of the base oil of Examples 2 are also listed in Table 2.

COMPARATIVE EXAMPLES

For reasons of comparison, the properties of the following commercial available base oils were determined and are also listed in Table 2: HVI 40 (obtained from Shell, Refinery Petit Couronne, France); HMVIP 40 (obtained from Deutsche Shell, Hamburg, Germany); Ultra S 2 (obtained from S-Oil Corporation, Seoul, Korea); and Sipmet 7 (obtained from SIP Ltd., London, Great-Britain).

As can be seen from Table 2, the base oils according to the present invention exhibit an excellent flash point and excellent evaporation loss at different temperatures.

TABLE 2 Oils treated Method unit Ex. 1 Ex. 2 HVI 40 HMVIP 40 Ultra S 2 Sipmet 7 Viscosity Index ASTM D 2270 123 120 93 86 114 99 Kinematic Viscosity ASTM D 445 mm²/s 7.823 7.987 8.002 7.598 7.097 7.715 @ 40° C. Kinematic Viscosity ASTM D445 mm²/s 2.361 2.383 2.285 2.188 2.184 2.255 @ 100° C. Flash Point (open) ASTM D 92 ° C. 183 186 166 160 160 164 Flash Point ASTM D 93 ° C. 175.5 178 157.5 148 148 155 (closed) Noack Volatility CEC L40 % 1.90 1.27 5.31 5.85 4.76 4.18 (at 150° C.) A93, modified Volatility @ 60° C. % 0.06 0.03 0.89 1.13 0.98 0.6 @ 80° C. 0.29 0.12 2.9 3.47 2.59 2.1 @ 100° C. 1.8 0.9 9.7 10.1 6.6 6.2 @ 120° C. 6.8 4.1 22.8 23.9 13.9 22.1 @ 140° C. 22.3 15.5 45.4 50.6 29.6 37.4 Pour point ASTM D 97 ° C. −54 −54 −21 −18 −37.5 −45

EXAMPLE 3

Some metal working fluid compositions according to the present invention were compounded, using at least 80 wt % of the base oils of Example 1 and 2 and using standard additives. The metal working fluids according to the present invention exhibited an excellent flash point and excellent evaporation loss at different temperatures. 

1. Metal working fluid comprising at least 80 wt % of a Fischer-Tropsch derived a base oil, the base oil having a viscosity index of more than 110 according to ASTM D 2270 and a pour point of less than −40° C. according to ASTM D 97, wherein the base-oil has a Noack Volatility at 150° C. of less than
 2. 2. Metal working fluid according to claim 1, wherein the base oil has a viscosity index of more than
 115. 3. Metal working fluid according to claim 1 or 2, wherein the base oil has a pour point of less than −50° C.
 4. Metal working fluid according to one or more of the preceding claims, wherein the base oil has a kinematic viscosity at 100° C. of between 1-4 mm²/s.
 5. Metal working fluid according to one or more of the preceding claims, wherein the base oil has a flash point of more than 170° C., according to ASTM D
 92. 6. Metal working fluid according to one or more of the preceding claims, wherein the base oil has a Delta Distillation value (95 wt %-5 wt %) of less than 130° C., preferably less than 100° C., even more preferably less than 95° C., the distillation values being determined according to ASTM D
 2888. 7. Metal working fluid according to one or more of the preceding claims, wherein the base oil has a Delta Distillation value (95 wt-5 wt %) of less than 100° C., the distillation values being determined according to ASTM D
 2888. 8. Metal working fluid according to one or more of the preceding claims, wherein the base oil is obtained by (a) hydrocracking/hydroisomerisating a Fischer-Tropsch product, (b) separating the product of step (a) into at least one or more fuel fractions and the base oil fraction.
 9. Metal working fluid according to claim 8, wherein the base oil is obtained by subjecting a fraction boiling above 350° C. as obtained in step (b) to a dewaxing step (c).
 10. Metal working fluid according to one or more of the preceding claims, wherein the metal working fluid comprises one or more additives.
 11. Use of the metal working fluid according to one or more of the preceding claims as a metal working fluid, in particular for high speed machining.
 12. Metal working method using a high speed rotary machine operating at a speed of above 8000 rotations per minute (RPM) wherein the rotary machine is provided with a rotatable hollow shaft through which the metal working fluid according to any one of claims 1-11 flows to a machine tool mounted on the shaft.
 13. Metal working method according to claim 12, wherein the metal working method is a high speed grinding operation in which the grinding operation is performed using a grinding stone at a speed of between 50 and 200 m/s.
 14. Metal working method according to any one of claims 12-13, wherein the metal working fluid is provided to the machine at a pressure of between 20 and 60 bar. 